Cooling is can be an important aspect in the design of any electrical product, such as IGBT (insulated gate bipolar transistor) based products, e.g., DC-breakers, as heat is inevitably generated by the current flowing through the electrical circuits. In recent years there has been a tendency of power electronic devices to reach larger and larger power values. This increase in power can be directly related to an increase in thermal energy dissipated by the power electronic devices. However, because power electronic devices still remain vulnerable to thermal problems more efficient cooling systems would be useful.
The further trend towards achieving higher power densities, which results in more compact power electronic devices being able to handle an equal or larger amount of power than before, as well as less space for the cooling system and for the air flow, pose continuous challenges to the design and cooling performance of the employed cooling systems.
Moreover, it is desired that cooling systems for modern electrical products have higher performance at a lower price.
At present, one way of providing an efficient cooling system for power electronic devices, such as IGBT (insulated gate bipolar transistor) based DC-breakers, is to provide a two-phase cooling circuit. Such a cooling circuit brings a liquid into thermal contact with the heat emitting device via an evaporating unit. The liquid is heated inside of the evaporating unit by the dissipated heat from the heat emitting device and reaches a boiling temperature. As the temperature of the liquid will not rise above the boiling temperature, the temperature of the liquid and therefore the temperature of the heat emitting device is kept at a temperature of the boiling point of the liquid as a maximum. The vapour of the liquid is then guided through a vapour riser pipe system to a condenser. Within the condenser the vapour is changed into a liquid by emitting heat. For example, in the condenser the heat is emitted to a coolant medium, such as air at ambient temperature. The vapour thus returns to its liquid phase. The condenser and the evaporating unit are connected via a liquid downcomer pipe system such that the condensed vapour is fed back to the evaporating unit as a liquid. Such a two-phase cooling system is, for instance, disclosed in EP 2 282 624, the entire content of which is incorporated herein by reference.
Two-phase cooling circuits provide increased cooling performance. However, due to the limited life-span and thermal vulnerability of power electronic devices improved two-phase cooling circuits can be useful, where improvements are directed to cooling efficiency. Further, due to the competitive nature of the market for such cooling circuits, increasing cooling efficiency at the same or a reduced cost is desired.